docs: def Q_weir_V_Shen(h1, angle=90):
      r'''Calculates the flow rate across a V-notch (triangular) weir from
      the height of the liquid above the tip of the notch, and with the angle
      of the notch. Most of these type of weir are 90 degrees. Model from [1]_
      as reproduced in [2]_.
  
      Flow rate is given by:
  
      .. math::
          Q = C \tan\left(\frac{\theta}{2}\right)\sqrt{g}(h_1 + k)^{2.5}
  
      Parameters
      ----------
      h1 : float
          Height of the fluid above the notch [m]
      angle : float, optional
          Angle of the notch [degrees]
  
      Returns
      -------
      Q : float
          Volumetric flow rate across the weir [m^3/s]
  
      Notes
      -----
      angles = [20, 40, 60, 80, 100]
      Cs = [0.59, 0.58, 0.575, 0.575, 0.58]
      k = [0.0028, 0.0017, 0.0012, 0.001, 0.001]
  
      The following limits apply to the use of this equation:
  
      h1 >= 0.05 m
      h2 > 0.45 m
      h1/h2 <= 0.4 m
      b > 0.9 m
  
      .. math::
          \frac{h_1}{b}\tan\left(\frac{\theta}{2}\right) < 2
  
      Flows are lower than obtained by the curves at
      http://www.lmnoeng.com/Weirs/vweir.php.
  
      Examples
      --------
      >>> Q_weir_V_Shen(0.6, angle=45)
      0.21071725775478228
  
      References
      ----------
      .. [1] Shen, John. "Discharge Characteristics of Triangular-Notch
         Thin-Plate Weirs : Studies of Flow to Water over Weirs and Dams."
         USGS Numbered Series. Water Supply Paper. U.S. Geological Survey :
         U.S. G.P.O., 1981
      .. [2] Blevins, Robert D. Applied Fluid Dynamics Handbook. New York, N.Y.:
         Van Nostrand Reinhold Co., 1984.
      '''
      C = interp(angle, angles_Shen, Cs_Shen)
      k = interp(angle, angles_Shen, k_Shen)    
      return C*tan(radians(angle)/2)*g**0.5*(h1 + k)**2.5